The present invention relates to a sputtering target of ferromagnetic material for use in the deposition of a magnetic thin film of a magnetic recording medium, and particularly for use in the deposition of a magnetic recording layer of a hard disk based on the perpendicular magnetic recording system; and to a sputtering target with low generation of particles which has large pass-through flux and enables a stable electrical discharge when sputtered with a magnetron sputtering device.
In the field of magnetic recording as represented with hard disk drives, a material based on Co, Fe or Ni as ferromagnetic metals is used as a magnetic-thin-film material which is used for the recording. For example, Co—Cr-based or Co—Cr—Pt-based ferromagnetic alloys comprising Co as its main component are used for the recording layer of hard disks based on the longitudinal magnetic recording system.
Moreover, composite materials of a Co—Cr—Pt-based ferromagnetic alloy comprising Co as its main component and nonmagnetic inorganic substances are often used for the recording layer of hard disks based on the perpendicular magnetic recording system which was recently put into practical application.
A magnetic thin film of a magnetic recording medium such as a hard disk is often produced by performing sputtering with a ferromagnetic sputtering target having the foregoing materials as its components in light of its high productivity.
As a method of manufacturing this kind of ferromagnetic sputtering target, the melting method or the powder-metallurgical method may be considered. It is not necessarily appropriate to suggest which method is better since it will depend on the demanded characteristics, but a sputtering target composed of a ferromagnetic alloy and nonmagnetic inorganic grains, which is used for forming the recording layer of hard disks based on the perpendicular magnetic recording system, is generally manufactured with powder metallurgy. This is because the inorganic grains need to be uniformly dispersed within the alloy basis material and this is difficult to achieve with the melting method.
For example, proposed are methods of inhibiting the generation of particles by achieving the feature that the amount of chrome oxide agglomerations with an absolute maximum length exceeding 5 μm is 500 agglomerations/mm2 or less in the basis metal of a sputtering target of Co-based sintered alloy for forming a magnetic recording film, and no chrome oxide agglomeration with an absolute maximum length exceeding 10 μm exists therein (Patent Documents 1 to 3).
The foregoing Documents describe that it will be possible to achieve such feature that the amount of chrome oxide agglomerations with an absolute maximum length exceeding 5 μm is 500 agglomerations/mm2 or less and no chrome oxide agglomeration with an absolute maximum length exceeding 10 μm exists, by using a Co—Cr alloy powder and/or a Cr—Pt alloy powder as raw powders. However, it might not be that the generation of particles can be sufficiently inhibited according to these Documents.
There are various types of sputtering devices, but a magnetron sputtering device comprising a DC power source is broadly used in light of its high productivity for the deposition of the foregoing magnetic recording films. The sputtering method is to place a positive-electrode substrate and a negative-electrode target opposite each other, and generate an electric field by applying high voltage between the substrate and the target under an inert gas atmosphere.
Here, inert gas is ionized, plasma composed of electrons and positive ions is formed, the positive ions in this plasma collide with the target (negative electrode) surface to discharge the constituent atoms of the target, and the extruded atoms adhere to the opposing substrate surface to form a film. The sputtering method employs a principle where the material configuring the target is deposited on the substrate as a result of performing the sequential process described above.    [Patent Document 1] Japanese Laid-Open Patent Publication No. 2008-24001    [Patent Document 2] Japanese Laid-Open Patent Publication No. 2008-88546    [Patent Document 3] Japanese Laid-Open Patent Publication No. 2007-291512